Front end: the Simplifier use-chain default flip (#23070) never applied to already-patched trees — the grep guard skips the updated patch, so dev boxes and helper-cache emitters still run the legacy O(phis×blocks) walk (re-#36225) (script/apply-patches.sh:560, patches/php-cfg-simplifier-use-chain.patch)

[PurHur]

Category

Foundation: · compiler throughput + patch mechanism · child of #36188 · respin of #36225 (closed by PR #36242, whose summary states "Use-chain is already the compile default via patches/php-cfg-simplifier-use-chain.patch on master" — true only for trees patched after 2026-07-25)

Problem

Verified on the maintainer's tree at master 4eed6a2785 after a fresh script/apply-patches.sh run today:

• patches/php-cfg-simplifier-use-chain.patch (updated ac1ac79e0d 2026-07-25, Perf: default PHPCFG Simplifier to use-chain path (#23056) #23070) makes use-chain the default with PHPCFG_SIMPLIFIER_LEGACY=1 as opt-out.
• The vendored vendor/ircmaxell/php-cfg/lib/PHPCfg/Visitor/Simplifier.php:209 still reads if ('1' !== getenv('PHPCFG_SIMPLIFIER_USECHAIN')) → legacy by default; grep -c "getenv('PHPCFG_SIMPLIFIER_LEGACY')" on it → 0.
• Cause: script/apply-patches.sh:560-562 treats the patch as applied when replaceVariablesByCfgWalk is present — a marker introduced by the July 5 version of the same patch (Speed up inventory lint: opt-in fast frontend patches + parallel cached bin/lint.php (#16077) #16394). Every tree patched between July 5 and July 25 (dev boxes, worktrees, the helper-cache emitter, the gen-0 refresh boxes) keeps the old code forever; only fresh composer install trees (CI) get the flip. Two different compilers by history.
• Measured cost on this tree: preprocessor on lib/Block.php 2,792 ms (legacy) vs 152 ms (use-chain) — 18x; the July 25 gen-0 OOM profile had 57 % of samples in the legacy walk on the very day the flip "landed".

PHP implementation target

• Guard by the new behaviour, not the old marker: patch_already_applied for this patch must require getenv('PHPCFG_SIMPLIFIER_LEGACY') in the file; same review for every guard that predates a patch update (git log -- patches/X.patch newer than the guard line).
• apply-patches.sh --verify-pristine (PR Fix php-llvm-structgep-assert.patch drift blocking CI (#36209) #36233) extended to all patches (see Foundation: patches/ are no longer the source of truth — apply-patches.sh is 7,508 lines with 85 overlay functions and 412 grep guards, 92 of 183 patches neither apply nor reverse cleanly; fork php-cfg/php-types and keep patches only for php-llvm (patches/, script/apply-patches.sh) #36229 for the fork direction).
• Re-run make helper-runtime-prelink-refresh after fixing the tree — the committed units may have been emitted by a legacy-Simplifier compiler (order-sensitive phi operand types, per the patch's own comment).

Done when

• On a tree patched before 2026-07-25, script/apply-patches.sh updates Simplifier.php to the use-chain default; php bin/vm.php -l lib/Block.php ≥ 30 % faster on this box
• A unit test asserts the vendored file matches the patch's post-image for this and every other patch (or --verify-pristine covers all 183)
• SimplifierUseChainOpcodeEquivalenceTest (fixed in Foundation: fix vacuous Simplifier use-chain equivalence test (#36225) #36242) green with the default flipped